Vehicle and engine control system and method

ABSTRACT

An engine control system controls engine torque to transition through the transmission lash zone. The transmission lash zone is determined using speed ratio across the torque converter. When near the transmission lash zone, engine torque is adjusted at a predetermined rate until the system passes through the transmission lash zone. By limiting the change of torque in this way, driveability is improved and it is possible to quickly and reliably provide negative engine torque for braking.

[0001] This application is a continuation of U.S. application Ser. No.09/416,433, filed Oct. 12, 1999, entitled “VEHICLE AND ENGINE CONTROLSYSTEM AND METHOD”.

FIELD OF THE INVENTION

[0002] The present invention relates to a system and method to controlan internal combustion engine coupled to a torque converter, and inparticular to adjusting engine output to improve drive feel.

BACKGROUND OF THE INVENTION

[0003] Internal combustion engines must be controlled in many differentways to provide acceptable driving comfort during all operatingconditions. Some methods use engine output, or torque, control where theactual engine torque is controlled to a desired engine torque through anoutput adjusting device such as with an electronic throttle, ignitiontiming, or various other devices. In some cases, such as during normaldriving conditions, the desired engine torque is calculated from theamount of depression of an accelerator pedal. In other conditions, suchas idle speed control, the desired engine torque is calculated based ona speed error between actual engine speed and a desired engine speed.Some attempts have been made to use this torque control architecture toimprove drivability during deceleration conditions such as when a driverreleases their foot to the minimum accelerator pedal position, known tothose skilled in the art as a tip-out. During a tip-out, the driver isindicating a desire for reduced engine output.

[0004] One system that attempts to use speed control during decelerationconditions operates the engine in such a way as to maintain constantengine speed during slow moving or stopped conditions. In this system,the engine is controlled to a constant speed taking into account theloading from the torque converter. The loading from the torque converteris calculated based on the engine speed and turbine speed. Engine speedcan be controlled to a constant level during deceleration to adsorbenergy from the vehicle and assists in vehicle braking. Further, asturbine speed increases, the desired engine speed is reduced to provideeven more engine braking. Such a system is described in DE 4321413A1.

[0005] The inventors herein have recognized a disadvantage with theabove approach. In particular, when the accelerator pedal is releasedand subsequently engaged, the prior art system exhibits poor drivabilitydue transmission gears lash. For example, when the engine transitionsfrom exerting a positive torque to exerting a negative torque (or beingdriven), the gears in the transmission separate at the zero torquetransition point. Then, after passing through the zero torque point, thegears again make contact to transfer torque. This series of eventsproduces an impact, or clunk, resulting in poor drivability and customerdissatisfaction. In other words, the engine first exerts a positivetorque through the torque converter onto the transmission input gears todrive the vehicle. Then, when using the prior art approach duringdeceleration, the engine is driven by the torque from the transmissionthrough the torque converter. The transition between these two modes isthe point where the engine is producing exactly zero engine braketorque. Then, at this transition point, the gears in the transmissionseparate because of inevitable transmission gear lash. When the gearsagain make contact, they do so dynamically, resulting in an undesirableimpact.

[0006] This disadvantage of the prior art is exacerbated when theoperator returns the accelerator pedal to a depressed position,indicating a desire for increased engine torque. In this situation, thezero torque transition point must again be traversed. However, in thissituation, the engine is producing a larger amount of torque than duringdeceleration because the driver is requesting acceleration. Thus,another, more severe, impact is experienced due to the transmission lashduring the zero torque transition.

SUMMARY OF THE INVENTION

[0007] An object of this invention is to provide a method fordetermining when the vehicle is operating in or near the transmissionlash zone.

[0008] The above object is achieved and disadvantages of priorapproaches overcome by a method for estimating when a vehicle is near atransmission lash zone, the vehicle having an internal combustion enginecoupled to a transmission via a torque converter having a speed ratiofrom torque converter output speed to torque converter input speed, themethod comprising the steps of: indicating when the speed ratio iswithin a predetermined range; and determining that the vehicle is nearthe transmission lash zone in response to said indication.

[0009] An advantage of the present invention is that it is possible tomake other engine control features aware that the vehicle is operatingin a region where transmission gear separation may occur. Thus, otherengine control features can take action to minimize effects oftransmission gear separation.

[0010] In another aspect of the present invention, an object is toprovide an engine output control system for easing transitions throughthe transmission lash zone.

[0011] The above object is achieved, and problems of prior approachesovercome, by a vehicle control method for a vehicle having an internalcombustion engine coupled to a torque converter, the torque converterhaving a speed ratio from torque converter output speed to torqueconverter input speed, the torque converter coupled to a transmission,the method comprising the steps of: indicating when the speed ratio iswithin a predetermined range; and in response to said indication,adjusting an operating parameter to control a change in an engine outputto be less than a preselected value.

[0012] By using signals already available, it is possible to provide areal-time estimate of the transmission lash zone, or zero torque point.With this information, it is then possible to transition through thetransmission lash zone gently by controlling engine output so that“clunk” is minimized and fuel economy and emissions are optimized. Inother words, the present invention utilizes the torque convertercharacteristics in the following way. Because these measurements arereadily available, adjusting engine output according to the presentinvention near the transmission lash zone allows much improved drivefeel since the effects of gear separation are minimized. Further, byusing turbine speed and engine speed, effects from road grade, vehiclemass, temperature, and other factors are inherently considered withoutcomplexity or addition computation.

[0013] An advantage of the above aspect of the invention is improveddrivability.

[0014] Another advantage of the above aspect of the invention isimproved customer satisfaction.

[0015] Yet another advantage of the above aspect of the invention isimproved fuel economy.

[0016] In yet another aspect of the present invention, the above objectsare achieved and disadvantages of prior approaches overcome by a controlmethod for a vehicle having an internal combustion engine coupled to atransmission via a torque converter having an input speed and an outputspeed, the method comprising the steps of: determining a speed ratioacross the torque converter based on said input speed and said outputspeed; and controlling an engine operating parameter at a preselectedrate when said speed ratio is within a predetermined range.

[0017] By controlling an operating parameter in this way, it is possibleto gently pass through the transmission lash zone, thereby improvingdriver comfort.

[0018] An advantage of the above aspect of the present invention isimproved drive comfort as a result of less severe transmission gearseparation.

[0019] Other objects, features and advantages of the present inventionwill be readily appreciated by the reader of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The object and advantages described herein will be more fullyunderstood by reading an example of an embodiment in which the inventionis used to advantage, referred to herein as the Description of thePreferred Embodiment, with reference to the drawings wherein:

[0021]FIG. 1 is a block diagram of a vehicle illustrating variouscomponents related to the present invention;

[0022]FIG. 2 is a block diagram of an engine in which the invention isused to advantage;

[0023]FIGS. 3-6 are high level flowcharts of various routines forcontrolling the engine according to the present invention; and

[0024]FIGS. 7A, 7B are a graphs of an example of operation according tothe present invention.

DESCRIPTION OF AN EMBODIMENT

[0025] Referring to FIG. 1, internal combustion engine 10, furtherdescribed herein with particular reference to FIG. 2, is shown coupledto torque converter 11 via crankshaft 13. Torque converter 11 is alsocoupled to transmission 15 via turbine shaft 17. Torque converter 11 hasa bypass clutch (not shown), which can be engaged, disengaged, orpartially engaged. When the clutch is either disengaged or partiallyengaged, the torque converter is said to be in an unlocked state.Turbine shaft 17 is also known as transmission input shaft. Transmission15 comprises an electronically controlled transmission with a pluralityof selectable discrete gear ratios. Transmission 15 also comprisesvarious other gears such as, for example, a final drive ratio (notshown). Transmission 15 is also coupled to tire 19 via axle 21. Tire 19interfaces the vehicle (not shown) to the road 23.

[0026] Internal combustion engine 10, comprising a plurality ofcylinders, one cylinder of which is shown in FIG. 2, is controlled byelectronic engine controller 12. Engine 10 includes combustion chamber30 and cylinder walls 32 with piston 36 positioned therein and connectedto crankshaft 13. Combustion chamber 30 communicates with intakemanifold 44 and exhaust manifold 48 via respective intake valve 52 andexhaust valve 54. Exhaust gas oxygen sensor 16 is coupled to exhaustmanifold 48 of engine 10 upstream of catalytic converter 20.

[0027] Intake manifold 44 communicates with throttle body 64 viathrottle plate 66. Throttle plate 66 is controlled by electric motor 67,which receives a signal from ETC driver 69. ETC driver 69 receivescontrol signal (DC) from controller 12. Intake manifold 44 is also shownhaving fuel injector 68 coupled thereto for delivering fuel inproportion to the pulse width of signal (fpw) from controller 12. Fuelis delivered to fuel injector 68 by a conventional fuel system (notshown) including a fuel tank, fuel pump, and fuel rail (not shown).

[0028] Engine 10 further includes conventional distributorless ignitionsystem 88 to provide ignition spark to combustion chamber 30 via sparkplug 92 in response to controller 12. In the embodiment describedherein, controller 12 is a conventional microcomputer including:microprocessor unit 102, input/output ports 104, electronic memory chip106, which is an electronically programmable memory in this particularexample, random access memory 108, and a conventional data bus.

[0029] Controller 12 receives various signals from sensors coupled toengine 10, in addition to those signals previously discussed, including:measurements of inducted mass air flow (MAF) from mass air flow sensor110 coupled to throttle body 64; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling jacket 114; a measurement ofthrottle position (TP) from throttle position sensor 117 coupled tothrottle plate 66; a measurement of transmission shaft torque, or engineshaft torque from torque sensor 121, a measurement of turbine speed (Wt)from turbine speed sensor 119, where turbine speed measures the speed ofshaft 17, and a profile ignition pickup signal (PIP) from Hall effectsensor 118 coupled to crankshaft 13 indicating an engine speed (N).Alternatively, turbine speed may be determined from vehicle speed andgear ratio.

[0030] Continuing with FIG. 2, accelerator pedal 130 is showncommunicating with the driver's foot 132. Accelerator pedal position(PP) is measured by pedal position sensor 134 and sent to controller 12.

[0031] In an alternative embodiment, where an electronically controlledthrottle is not used, an air bypass valve (not shown) can be installedto allow a controlled amount of air to bypass throttle plate 62. In thisalternative embodiment, the air bypass valve (not shown) receives acontrol signal (not shown) from controller 12.

[0032] Referring now to FIG. 3, a routine for detecting decelerationconditions is described. First, in step 310, driver actuated pedalposition (PP) is compared with calibratable item (PP₁₃CT), whichrepresents the pedal position at which the pedal is closed. In analternate embodiment, calibratable item (PP₁₃CT) represents the pedalposition below which a tip-out is indicated.

[0033] Alternatively, driver desired wheel torque, which is known tothose skilled in the art to be a function of pedal position and vehiclespeed, can be compared with a minimum desired wheel torque clip belowwhich deceleration is desired. When the answer to step 310 is YES, thenin step 312, both engine speed (N) and turbine speed (Wt) are read. Instep 314, a determination is made as to whether engine speed is greaterthan turbine speed. When the answer to step 314 is YES, thendeceleration conditions have been detected as shown in step 316.

[0034] Referring now to FIG. 4, a routine for calculating a desiredengine speed during deceleration conditions is described. First, in step406, a determination is made as to whether deceleration conditions havebeen detected. When the answer to step 406 is YES, a determination ismade in step 408 as to whether the torque converter is in and unlockedstate. When the answer to step 408 is YES, engine speed (N) is read andturbine speed (Wt) is read from turbine speed sensor 119 in step 410.Then, in step 414 the engine is controlled based on a speed ratio, SR asdescribed later herein with particular reference to FIG. 5. Speed ratiois determined as (SR=Wt/N) based on the turbine speed and engine speed.In other words, in this example, torque converter input speed is enginespeed and torque converter output speed is turbine speed. These speedsmay determined in various other ways such as, for example, turbine speedcan be determined from gear ratio and vehicle speed. Also, note that thespeed ratio may also be determined as (SRalt=N/Wt). Those skilled in theart will recognized that the present invention can be suitably reducedto practice in view of this disclosure using the speed ratio calculatedin either way.

[0035] Referring now to FIG. 5, a routine for controlling an engineoutput, engine torque in this case, is described. First, in step 510,speed ratio limit values (SR1, SR2) are determined based on engineoperating conditions. In a preferred embodiment, these values arecalculated based on vehicle speed and gear ratio using calibrationfunctions. However, various other signals may be used. These limitvalues (SR1, SR2) represent the upper and lower speed ratio valuesbetween which engine torque change is limited. In other words, accordingto the present invention, limit values (SR1, SR2) represent the upperand lower speed ratio values between which the zero torque transition,or transmission lash zone transition, occurs.

[0036] Continuing with FIG. 5, in step 511, a desired engine torque(Tdes) is determined using methods known to those skilled in the art.For example, desired engine torque may be determined based on a drivercommand, traction control, idle speed control, or various other methods.Also, desired engine torque can be either a desired indicated enginetorque, or a desired engine brake torque. Then, in step 512, adetermination is made as to whether speed ratio (SR) is within limitvalues (SR1, SR2). When the answer to step 512 is YES, then the enginetorque change is limited as now described and it is determined that thevehicle is operating near the transmission lash zone, or zero torquepoint. In step 514, a determination is made as to whether desired enginetorque change is greater than change limit R1. In particular, adetermination is made as to whether the absolute value of desired enginetorque change is greater than change limit R1. Change limit R1 isdetermined based on engine operating conditions such as, for example,engine speed, turbine speed, vehicle speed, gear ratio, or othervariables. In a preferred embodiment, Change limit R1 is determinedbased on vehicle speed using a calibrated function. Also in a preferredembodiment, a rate of change of desired engine torque is determinedbased on current desired engine torque (Tdes _(i)) , previous filtereddesired engine torque (Tdesf_(i-1)) and sample time (Dt) as:$\frac{\Delta \quad {Tdes}}{\Delta \quad t} = {\frac{{Tdes}_{i} - {Tdesf}_{i - 1}}{t_{i} - t_{i - 1}}.}$

[0037] When, the answer to step 514 is YES, in step 516, currentfiltered desired engine torque (Tdesf_(i)) is set equal to currentdesired engine torque (Tdes_(i)). Otherwise, in step 518, currentfiltered desired engine torque (Tdesf_(i)) is calculated based onprevious filtered desired engine torque (Tdesfi_(i-1)) and change limitR1 as:${Tdesf}_{i} = {{Tdesf}_{i - 1} + {{R1}*\Delta \quad t*{{{sgn}\left( \frac{\Delta \quad {Tdes}}{\Delta \quad t} \right)}.}}}$

[0038] The function (sgn) is known to those skilled in the art as thesign function, which produces a positive unity value when the parameter$\left( \frac{\Delta \quad {Tdes}}{\Delta \quad t} \right)$

[0039] is positive, and a negative unity when the parameter$\left( \frac{\Delta \quad {Tdes}}{\Delta \quad t} \right)$

[0040] is negative. Then, from either step 516 or 518, in step 520,actual engine torque is controlled to filtered desired engine torque(Tdesf_(i)). Those skilled in the art will recognize various methods ofcontrolling actual engine torque to a desired value such as, forexample, by adjusting throttle position, adjusting airflow, adjustingexhaust gas recirculation, adjusting ignition timing, adjusting camtiming, or adjusting fuel injection amount.

[0041] Those skilled in the art will recognize various other methods, inview of this disclosure, for limiting an engine output change. Accordingto the present invention, any method can be used for limiting the engineoutput change while in or near the transmission lash zone withoutdeparting from the spirit and scope of the invention. For example, in analternate embodiment, engine speed change can be limited while in ornear the transmission lash zone.

[0042] Those skilled in the art will also recognize various othermethods, in view of this disclosure, for filtering a parameter. Forexample, low pass filters, notch filters, and various other filters canbe used to limit the amount of change of a parameter. In other words,desired engine torque can be low pass filtered when speed ratio (SR) iswithin limits (SR1,SR2).

[0043] In an alternative embodiment, an engine control parameter, suchas a throttle position, may be substituted for engine torque asdescribed in FIG. 6.

[0044] Referring now to FIG. 6, in step 610, speed ratio limit values(SR1, SR2) are determined based on engine operating conditions. Then, instep 611, a desired throttle position (TPdes) is determined usingmethods known to those skilled in the art. For example, desired throttleposition may be determined based on a driver command, traction control,idle speed control, or various other methods. Then, in step 612, adetermination is made as to whether speed ratio (SR) is within limitvalues (SR1, SR2). When the answer to step 612 is YES, then the throttleposition change is limited as now described. In step 614, adetermination is made as to whether desired throttle position change isgreater than change limit R2. Change limit R2 is determined based onengine operating conditions such as, for example, engine speed, turbinespeed, vehicle speed, gear ratio, or other variables. In a preferredembodiment, Change limit R2 is determined based on vehicle speed using acalibrated function. Also, in a preferred embodiment, a rate of changeof desired throttle position is determined based on current desiredthrottle position (TPdes_(i)) and previous filtered desired throttleposition (TPdesf_(i-1)) as:$\frac{\Delta \quad {Tdes}}{\Delta \quad t} = {\frac{{Tdes}_{i} - {Tdesf}_{i - 1}}{t_{i} - t_{i - 1}}.}$

[0045] When, the answer to step 614 is YES, in step 616, currentfiltered desired throttle position (TPdesf_(i)) is set equal to currentdesired throttle position (TPdes_(i)). Otherwise, in step 618, currentfiltered desired throttle position (TPdesf_(i)) is calculated based onprevious filtered desired throttle position (TPdesf_(i-1)) and changelimit R2 as:${TPdesf}_{i} = {{TPdesf}_{i - 1} + {{R2}*\Delta \quad t*{{{sgn}\left( \frac{\Delta \quad {TPdes}}{\Delta \quad t} \right)}.}}}$

[0046] Then, from either step 616 or 618, in step 620, actual throttleposition is controlled to filtered desired throttle position(TPdesf_(i)). Those skilled in the art will recognize various methods ofcontrolling actual throttle position to a desired value such as, forexample, by using a controller based on a throttle position errorsignal.

[0047] Referring now to FIGS. 7A and 7B, these graphs shows an exampleof operation according to the present invention. In this example, upperand lower limit values are set to (SR2=1.05, SR1=0.95). FIG. 7A showsdesired engine torque on the vertical axis and time on the horizontalaxis. The dashed line shows desired engine torque and the solid lineshows the filtered desired engine torque according to the presentinvention. At time t2, the speed ratio reaches limit value SR1. Fromthis point, the desired engine torque is limited to change at a maximumrate of R1. Then, the speed ratio reaches limit value SR2 at time t2 andthe filtered desired engine torque again equals the desired enginetorque. FIG. 7B shows the corresponding transmission input shaft torque(which is equal to torque converter output shaft torque). Astransmission input shaft torque passes through zero torque, or thetransmission lash zone, torque is changing slow than it would otherwisebe, and transmission gear separation effects are minimized.

[0048]FIGS. 7A and 7B have shown an example of operation according tothe present invention for tip-out conditions. However, those skilled inthe art will recognize that the present invention as described can alsobe used to advantage during tip-in maneuvers, tip-out maneuvers, orboth.

[0049] In addition to the above control methods, other features can beperformed. In particular, when at a speed ratio of substantially one,controller 12 has determined that the engine drive train is producingsubstantially zero torque as long as the torque converter is unlocked.Thus, if torque sensor 121 has a tendency to drift, it can be re-zeroedin response to an indication that the drive train is producingsubstantially zero torque.

[0050] This concludes the description of the Preferred Embodiment. Thereading of it by those skilled in the art would bring to mind many otheralterations and modifications without departing from the spirit andscope of the invention. For example, if turbine speed is not measured,vehicle speed and gear ratio can be substituted without loss offunction. Accordingly, it is intended that the scope of the invention belimited by the following claims.

We claim:
 1. A method for controlling a vehicle having an internalcombustion engine coupled to a transmission via a torque converterhaving a torque converter output speed and a torque converter inputspeed, the method comprising: indicating the torque converter isunlocked and torque converter output speed is less than torque converterinput speed; and in response to said indication, controlling a change inan engine output to be less than a preselected value until torqueconverter output speed is greater than torque converter input speed orthe torque converter is locked.
 2. The method recited in claim 1 whereinsaid engine output is engine torque.
 3. The method recited in claim 1wherein said predetermined range is between a lower limit value and anupper limit value.
 4. The method recited in claim 3 wherein said lowerlimit value and said upper limit value are each based on engineoperating conditions.
 5. The method recited in claim 1 wherein saidpreselected value is based on operating conditions.
 6. The methodrecited in claim 1 wherein said preselected value is based on engineoperating conditions.
 7. A method for controlling a vehicle having aninternal combustion engine coupled to a transmission via a torqueconverter torque having a speed ratio between torque converter outputspeed and a torque converter input speed, the method comprising:indicating when the speed ratio is within a predetermined range and thetorque converter is unlocked; and determining when the engine isproducing substantially zero output in response to said indication. 8.The method recited in claim 7 further comprising measuring the torqueconverter output speed and the torque converter input speed, anddetermining the speed ratio based on said measured torque converteroutput speed and torque converter input speed.
 9. The method recited inclaim 7 further comprising controlling the engine output by adjustingengine airflow.
 10. The method recited in claim 9 further comprisingcontrolling the engine airflow by adjusting a throttle coupled to theengine.
 11. The method recited in claim 7 further comprising resetting atorque sensor zero based on said determination.
 12. The method recitedin claim 7 wherein said indication further includes an indication of adeceleration condition.
 13. The method recited in claim 12 wherein saiddeceleration condition is based on an operator command.
 14. A systemcomprising: an engine; a transmission; a torque converter coupling saidengine to said transmission; and a computer storage medium having acomputer program encoded therein for controlling at least the engine,said computer storage medium comprising; code for controlling a changein an engine output to be less than a preselected value while torqueconverter output speed transitions from less than torque converter inputspeed to greater than torque converter input speed.
 15. The systemrecited in claim 14 wherein said computer storage medium furthercomprises code for measuring torque converter input speed and torqueconverter output speed.
 16. The system recited in claim 14 wherein saidcomputer storage medium further comprises code for controlling a changein an engine output to be less than a preselected value in response toan indication that said torque converter is unlocked.
 17. The systemrecited in claim 14 wherein said engine output is engine torque.
 18. Anarticle of manufacture, comprising: a computer storage medium having acomputer program encoded therein for controlling an engine coup led to atransmission via a torque converter, said computer storage mediumcomprising; code for controlling a change in an engine output to be lessthan a preselected value while torque converter output speed transitionsfrom less than torque converter input speed to greater than torqueconverter input speed and said torque converter is unlocked.
 19. Thearticle recited in claim 19 wherein said engine output is engine torque.